how many cories in a 55g

While it would depend in part on the species (bronze and greens get bigger than skunks and pandas, for example), the other bottom dwellers you have, and the total stocking plan for the tank, I'd say you could have 5-7 easily. If there aren't any other bottom dwellers, and the mid and top level fish are lightly stocked, then you can have probably 7-11 easily.

I have 7 Corydoras leucomelas in my 55g. They are about 1.5-2" each and I could probably afford to add a couple more. The only other bottom feeder in the tank is a 6" pleco. Be sure to keep them in a group, at least 4-5, and give them some plants and other hiding places. They will be a lot more active in larger groups and also if they have hiding spots available.

10